José Marchese

Fouling behaviour of polyethersulfone UF membranes made with different PVP

Abstract Several polyethersulfone (PES) ultrafiltration membranes have been made with small quantities of polyvinyl-pyrrolidone (PVP) of different molecular weights to increase the permeability without a significant reduction in selectivity. The corresponding fouling mechanism and subsequent structural modifications have been analyzed when in contact with bovine serum albumin (BSA) and dl -histidine (DLH). It has been shown that according to the relative sizes of solute and pores of the membranes: BSA fouls the three membranes externally whereas DLH fouls them internally. Moreover, BSA fouls the non-PVP membranes faster than DLH fouls them slower, according to the action of hydrophobic and electrostatic forces acting at the working pH (4.9). The changes in structure, remaining after water rinsing, is quite similar for the three membranes and both the solutes, as obtained by a r etention test of adequate polyethylene glycols (PEGs).

Pore size distributions based on AFM imaging and retention of multidisperse polymer solutes: Characterisation of polyethersulfone UF membranes with dopes containing different PVP

Abstract Several polyethersulfone ultrafiltration membranes have been made with small quantities of polyvinyl-pyrrolidone of different molecular weights. Our aim was to increase the permeability without significant changes in selectivity. Different approaches to get effective pore size distributions have been compared between them and with the topographic results obtained from atomic force microscopy (AFM) image analysis. In particular, the use of cumulative retention coefficients have proved to be preferable to adequately obtain effective pore size distributions based on retention of multidisperse solutions. Within this frame, it has been proved that small PVP content of the studied membranes leads to different increasing permeabilities with very similar selectivities.

Ultrafiltration of vegetable oils: Degumming by polymeric membranes

Abstract In this work, four different membranes synthesized in our laboratories have been tested for their permeation flux, phospholipid retention and stability in hexane during membrane degumming of crude soybean oil. Membranes were made of three different polymeric materials, i.e. Polyvinylidenfluoride (PVDF), Polyethersulfone (PES) and Polysulfone (PSf), and prepared by the phase inversion process. Raw membranes were characterized by the molecular weight cut-off (MWCO) and the water permeability, L h,w . Ultrafiltration (UF) of an oil–hexane miscella was performed in a stirred dead-end UF cell, pressurized with N 2 . All membranes were soaked in solvent of decreasing polarities to minimize the action of solvent on pore size. Each membrane was tested with pure solvent first and the membrane permeability to pure hexane, L h,h , was determined. The degumming experiments were carried out with a 25% crude soybean oil–hexane mixture right after the pure solvent test. The ratio ( L h,h / L h,w ) is used to indicate the degree of change in membrane structure due to the organic solvent. Results show that PVDF is more stable with hexane than PES and PSf. In addition to membrane material, pore size influences membrane stability also. Small pore sizes give more stable membranes. During degumming, a sharp decrease in the permeate flux with time occurs at the beginning of the permeation process. This behaviour is explained in terms of concentration polarization effects and internal fouling. PES and PSF membranes have a larger initial decrease than PVDF ones.

Selective separation of copper with Lix 864 in a hollow fiber module.

The transfer and separation of Cu(II), Co(II), Ni(II) and Zn(II) ions across a hollow fiber supported liquid membrane containing LIX 864 as the mobile carrier dissolved in kerosene solvent has been investigated. The flux and selectivity for copper has been studied as a function of the feed flow, the carrier concentration in the liquid membrane and the extraction solution acidity. A maximum copper recovery at 30% of LIX (v/v) in the diluent was obtained. The permeation experiments showed that at pH 2 in the extraction solution a highly selective separation of Cu over the other cations can be achieved. Increasing the acidity of the extraction solution copper selectivity decrease and the grade of recuperation sequence is Cu>Co>Ni>Zn. These results suggest that in selected situations, this membrane system can be competitive with the conventional liquid-liquid extraction process, in particular in leaching solutions with low metal concentration.

Coupled transport of copper through different commercial supports containing LIX 984 as carrier

The coupled transport of copper(II) ions through a supported liquid membrane containing LIX 984 as the mobile carrier dissolved in kerosene has been studied. Many commercial membrane supports were investigated at different stirrer speeds in a permeation cell. An equation describing the permeation rate has been derived, taking into account stagnant layer aqueous diffusion and liquid membrane diffusion. By means of this treatment the copper overall transfer resistance and the experimental determination of the effective porosity factor (e/τ), for each support have been performed. The Accurel® 2E-PP membrane showed a relatively high value of e/τ (0.91), which makes this membrane an adequate support when the transport properties of the supported liquid membrane are concerned.

PVDF/PMMA membranes for lemon juice clarification: fouling analysis

Microfiltration/ultrafiltration membranes with different degrees of hydrophilicity and structural characteristics from poly(vinylidene fluoride) (PVDF), polymethylmetacrylate (PMMA), and polyvinylpirrolidone (PVP) in dimethylformamide (DMF) solvent were prepared to be used in the lemon juice clarification. The effect of transmembrane pressure (Δp= 0.4‐1 bar) and tangential feed velocity (v = 0.2‐1 m/s) on permeate flux and juice quality at T= 20˚C was examined. The membrane containing 15% of PVDF, 5% PMMA, and 5% PVP (mean pore radii rpm= 0.25 μm and porosity e= 0.25) achieved the best performance at Δp= 1 bar and v= 1 m/s, with a final permeate flux at quasi-steady state of 32.5 (L/hm 2 ). The clarified lemon juice presented physical, chemical, and nutritional characteristics comparable to the fresh lemon juice, and 100% of total solid rejection. Membrane fouling was evaluated by applying different fouling models. Results indicated that a good fitting correlation between the experimental data and both complete blocking and cake models was achieved.

Behavior of Araujiain, a new cysteine phytoprotease, in organic media with low water content

In this paper we studied the effect of different organic solvents (1-octanol, trichloroethylene, ethanol, ethyl acetate, tetrahydrofuran, cyclohexane, propanone, acetonitrile, dichloromethane, chlorobenzene, N,N-dimethylformamide, acetophenone, diethyl ether, methanol, ethylene glycol and toluene) with low and constant water content on substrate preferences, thermostability and stability (caseinolytic activity retention after 4 h) of proteases of Araujia hortorum Fourn. ( Asclepiadaceae ). The stability of araujiain was high in N,N-dimethylformamide and ethanol at 40oC, but decreased at higher temperature. Araujiain substrates preferences in buffer Tris-HCl (pH 8), ethylene glycol and N,N-dimethylformamide exhibited different patterns, but the enzyme showed a high preference by glutamine derivative in all cases. According to FTIR spectroscopy studies, araujiain changed its secondary structure and as a consequence, it also changed its substrate preferences. This enzyme showed lower α-helical character and greater β-sheet folding in buffer than in organic media. A larger amount of antiparallel β-sheet residues indicates the formation of tighter intermolecular hydrogen bonds and enzymatic aggregates. These facts could explain the higher esterolytic activities, the greater stability and good hydrolytic potential of araujiain in some organic media such as N,N-dimethylformamide.